hydrothermal ventA fissure on the floor of a sea out of which flows water that has been heated by underlying magma. The water can be as hot as 400°C (752°F) and usually contains dissolved minerals that precipitate out of it upon contact with the colder seawater, building a stack of minerals, or chimney. Hydrothermal vents form an ecosystem for microbes and animals, such as tubeworms, giant clams, and blind shrimp, that can withstand the hostile environment. ◇ The hottest hydrothermal vents are called black smokers because they spew iron and sulfide which combine to form iron monosulfide, a black compound.